square roots and negative infinity

problem:

Find the limit. (If you need to use -http://www.webassign.net/images/infinity.gif or http://www.webassign.net/images/infinity.gif, enter -INFINITY or INFINITY.)

http://www.webassign.net/cgi-bin/sym...%204%20x%29%29

I would explain what ive done in more detail, but i know im missing something due to x approaching neg. infinity, but i did multiply the above funct. by its conjugate to get (x-1)/(x-square root of x^2+4x). How would i go about this? Thank you. -Evan